The program applies early detection procedures to the study of lower extremity deep venous thrombosis and its complications (post- phlebitic syndrome and pulmonary embolism). A Doppler ultrasound blood flow velocity detection procedure is being used in combination with clinical evaluation in an epidemiologic study of venous disease in hospitalized patients. This involved a prevalence and incidence study in surgical patients and a proposed course of disease study in "high risk" individuals. The intent of the program is to obtain epidemiologic data about venous disease and its complications. The identification and evaluation of risk factors is emphasized. The value of computer- assisted risk factor analysis in management will be assessed.